Compared with the M13 system, T7 phage can directly cleave host bacteria, in no need of the secretion process. In the T7 phage display system, phages can be developed within only three hours, saving plenty of time. Besides, for polypeptides with over 50 amino acids, T7 phages can be assembled without helper phages. Importantly, T7 phages perform very stably under the conditions of high PH value, high salt, denatured agents (100 mmol/L DTT), etc. They can be screened under various conditions according to different needs, and maintain high screening activity even after screening.